Place a small ruler inside of your jar. Affix it to the inside of the neck with modeling clay.
Fill the jar with a few inches of isopropyl alcohol.
Place a straw into a bottle of isopropyl alcohol, so that the straw is half-submerged, and then plug the top end of the straw with modeling clay to form a seal. Afterwards, remove the straw.
Place the straw inside the jar, next to the ruler, and set it into place with clay. The bottom of the straw should enter the pool of isopropyl alcohol, but without touching the bottom of the jar.
Measure the level of alcohol in the straw daily. Rising atmospheric pressure will force down the alcohol in the jar while sending it up the straw, and vice versa.
Things You Will Need
- Small glass jar
- Modeling clay
- Isopropyl alcohol
- Try to leave the jar in a place that is neither too sunny, nor too drafty.